Live migration of a virtual machine: Live Migration (also known as dynamic migration or real-time migration), i.e., save/restore of a virtual machine, which means completely saving a running state of the whole virtual machine, and meanwhile, quickly restoring the virtual machine on a hardware platform with the same configuration as the original hardware platform or even a different hardware platform. After restoration, the virtual machine will still run smoothly, and a user will not notice any difference. Currently, major live migration technologies include XenMotion, VMotion of VMware, Hyper-V Live Migration of Microsoft, and the like.
Generally, in a process of migrating a virtual machine from a (source) physical machine to another (destination) physical machine, memory of the source virtual machine needs to be copied to the destination, and during copying, the memory of the source virtual machine constantly changes. Therefore, the source virtual machine needs to be suspended finally, that is, an operating system suspends operations on processes of the source virtual machine, so that the memory of the source virtual machine does not change any more. Moreover, all “dirty memory” of the source virtual machine is copied to the destination, to keep memory of a destination virtual machine the same as that of the source, so that a state of the virtual machine restored at the destination remains the same as the state before suspension. Restarting the virtual machine at the destination after the source virtual machine is suspended needs a period of time, and in this period, the virtual machine is unusable. Duration of this period is related to the size of “dirty memory” of the virtual machine that is copied in the final round, and when the “dirty memory” is relatively large, the final round of copying takes a relatively long time, and thus the virtual machine is unusable in a relatively long time. Therefore, a Transmission Control Protocol (TCP) connection inside the virtual machine receives no data packet from a peer in a longer time, and the peer does not receive any response from the migrated virtual machine in an even longer time. A timeout retransmission interval of the TCP doubles each time, and in this case, it takes a longer time to restore the TCP connection.
However, in the virtual machine live migration technologies in the conventional techniques, there is no method for rapidly restoring a TCP connection, and the only option is to wait for timeout retransmission of the connection or establish a new connection again.